1. Field of the Invention
The present invention relates to an anesthesia ventilation system for assisting or controlling patient breathing and more particularly to a pressure relief and volume control valve mechanism incorporated in an expandable bellows in an anesthesia system.
2. Description of the Prior Art
An anesthesia ventilator system is used to maintain adequate ventilation and better anesthesia control during surgery. An anesthesia ventilation system typically includes an expandable bellows that is connected to a patient breathing circuit, with patient breathing being controlled by the controlled expansion and contraction of the bellows. Typically, the bellows is housed in a closed chamber or canister, and a mechanical pressure control device controls the pressure in the canister so as to cause inflation and of the bellows.
A ventilator system used for anesthesia administration also can be used for other gas balance breathing systems, such as in an intensive care gas ventilator system. As used herein the term "anesthesia ventilator system" shall include such other systems involving a continuous flow of gas into a closed or semiclosed system.
In using any constant flow anesthesia system to assist patient breathing, it is important that pressure not be allowed to build up in the system so as to impair patient breathing. Similarly, it is important that the volume of gas contained in the bellows be limited to a predetermined amount so that forced inhalation does not exceed the patient's lung capacity. These controls are particularly necessary when an anesthesia ventilator device is used to control patient breathing in veterinary medicine, wherein the lung capacities of small animals are much smaller than those of humans and vary widely among different animals. Without proper control of ventilation pressure and volume, the administration of anesthesia to a small animal can easily result in cardiopulmanary complications.
In conventional anesthesia apparatus, it is customary to include a relief valve in the patient breathing circuit to limit pressure build up in that circuit. However, when a ventilator is used to control patient breathing, the operation of such a relief valve does not provide satisfactory pressure control in the system.
It is an object of the present invention to provide an improved anesthesia system particularly adapted to inhalation anesthesia of small animals that provides increased pressure and volume control by means of a simple and inexpensive control mechanism. Another object of the present invention is to make such a control apparatus compatible with a positive end expiratory pressure system.